The invention disclosed herein relates generally to an apparatus and method of forming pigment pseudoparticles from pigment particles, as well as the pigment pseudoparticles produced therefrom. More specifically, embodiments of the disclosed invention relate to polarizing pigment particles and agglomerating the polarized pigment particles to form pigment pseudoparticles.
Titanium dioxide pigment particles, iron oxides pigment particles, pearlescent pigment particles, other metal oxide pigment particles, are often used in cosmetics, detergents, paint, plastics, and other products and industries where it is desired to add to the color of the product and/or opacify the desired product. This is usually done through intensive mixing of pigment pellets and/or powder in a liquid medium to be colored. Some desired properties for the pigment pellets are the dispersability of the pigment throughout the application system, ease of bulk handling, ease of metering and the amount of dust tainting the pigment pellet.
To enhance dispersability in a medium to be colored, pigment is often produced in the form of a finely divided powder of preferably inorganic pigment particles. The powders are usually jet-milled, sand milled, hammer milled or roller milled as a finishing step in their production, which contributes to dispersability and gloss. However, milled pigments in the art generally exhibit poor dry flow characteristics and have the great disadvantage of being extremely dusty. During use of these powders, costly measures must be taken to reduce the harmful effects of the dust (e.g. workplace safety, ecological concerns, product quality assurance, etc.), thus consuming valuable time, money and other resources. Furthermore, pellets made from such powders are general difficult to handle, storing, transport and introduce into the manufacturing equipment without the pellets crumbling. Thus, products that have achieved good pigment dispersability often fail to provide good pigment stability and products that have achieved good pigment stability often fail to provide good pigment dispersability.
Processes of the prior art attempted to solve some of these problems by using chemical additives. For example, U.S. Pat. No. 4,285,994 (“Pearce”) discusses a process for production for free flowing dust-free pigments, a process comprising tumbling together a finely divided wax composition a powdered pigment so that the wax absorbs the pigment, and a nucleated pigment comprising a spray-chilled wax composition. Also, U.S. Pat. No. 4,375,520 (“Pennie”) discusses treatment of particles with a solid low-molecular weight polymer and a liquid polymer substance.
Other problems repeatedly experienced in handling large quantities of powders are caking, rat holing and bridging. The stability of pigment is important for good storage and transporting, and it is desired to avert aging and/or pigment clumping into undesired agglomerates when stored pigment is subjected to heat, humidity and pressure over time. Together with dust-related problems associated with finely divided powders, it is frequently desired that pigment particles are formed into pigment pellets. However, pigment pellets must also be formed so that they are easily dispersible in a medium and so the pellets do not clog feed bines, which causes reduced pigment flow and other problems.
Solutions to some of these problems have been attempted in the prior art. For example, U.S. Pat. No. 5,604,279 (“Bernhardt”) discusses a colorant composition consisting essentially of a free flow agent with one or more colorants finely dispersed in an amorphous poly-.alpha.-olefin which is composed of at least two different monomers having a butene-1 content of at least 25% by weight. U.S. Pat. No. 5,199,986 (“Krockert”) discusses a process for coloring building materials with inorganic pigments which comprises incorporating into said materials pigments in the form of granulates which are free-flowing and no dust forming wherein the pigment granulates are produced from spray dried granules by after-granulating.
Dispersability is a measure of the ease with which the pigment can be uniformly and homogenously mixed into a medium, and poor dispersion in the medium can cause large agglomerates that may result in lumps, surface imperfections, color streaks, non-uniform coloration, and/or incomplete color development within the medium. Methods of the prior art have attempted to enhance dispersability or to improve dry flow characteristics by surface treatment of pigments to achieve improved performance characteristics for when the pigment is dispersed in, for example, coatings and/or plastic compositions. For example, U.S. Pat. No. 3,925,095 (“Bockmann”) discusses a dispersible composition comprising an inorganic pigment or filler and a hydroxyalkylated alkylene diamine, while U.S. Pat. No. 4,056,402 (“Guzi”) discusses a pigment composition prepared by milling the pigment in water in the presence of a nonionic dispersing agent, mixing the milled pigment dispersion with a cellulose ether, and removing the water from the resulting mixture.
U.S. Pat. No. 4,310,483 (“Dorfel”) discusses a process for producing a granulate by thermal tumbling granulation utilizing an additive and a granulating auxiliary, and U.S. Pat. No. 4,464,203 discusses concentrated pigment formulations containing pigments and ethylene oxide. Pigments have also been treated with waxes, aqueous solutions, polymers, etc. For example, U.S. Pat. No. 4,127,421 (“Ferrill”) discusses the forming of an aqueous slurry of a lead chromate-containing pigment dispersed in a friable hydrocarbon resin. Also, U.S. Pat. No. 4,762,523 discusses mixing a long-chain polyester surfactant produced by condensation and adding an essentially non-volatile liquid selected from the group consisting of mineral oil and molten wax.
Another method for making free-flowing powders with low dust can be obtained by spray drying. These products generally exhibit poor coloring properties and end users have thus generally had to choose between free-flowing, low dusting, spray-dried pigments with poor coloring properties, and dusty, milled pigments with poor flow characteristics For example, U.S. Pat. No. 3,660,129 (“Luginsland”) discusses coating titanium oxide pigments with hydrous oxides and sanding and drying the pigment. This results in small particle size with a high proportion of fine particles that are not directly usable pellets. Also, this hydrophobic spray-drying post-treatment results in particles that have somewhat good flow properties but produce exceptionally large quantities of dust.
Other patents relating to spray drying include the Krockert patent discussed above, as well as U.S. Pat. No. 4,810,305 (“Braun”) and U.S. Pat. No. 5,035,748 (“Burrow”), which both discuss the use of organosiloxanes. Furthermore, U.S. Pat. No. 5,733,365 (“Halko”) discusses the aqueous milling, surface treatment, and spray-drying of inorganic pigments, U.S. Pat. No. 6,132,505 discusses spray drying and agglomeration, and U.S. Pat. No. 5,908,498 (“Kauffman”) discusses forming a dispersed slurry of pigment and water, milling the slurry and depositing a treating agent on the slurried milled pigment.
Each of the methods and products of the prior art are deficient in at least one of the characteristics desired of pigment, as the quality of the other characteristics increases. The prior art fails to solve the problem of forming a pigment pellet that simultaneously possesses the qualities of being extremely friable, highly dispersible, smoothly discharging, able to alleviate bridging and rat holing, substantially free of dust, easily metered, highly dense and resistant to compaction.
Pigment particles, such as titanium dioxide for example, generally have detrimental clumping properties due to the high cohesive nature of the pigment, the particles tightly clumping and caking during movement in transit, in storage. In use however, titanium dioxide forms fine powders or dusts which spread in the air, and which further stick to the surrounding areas. Any reduction in dust has serious health benefits and as well as other benefits relating to the concerns of the National Institute of Occupational Safety and Health (NIOSH), the Department of Labor and/or the Environmental Protection Agency. There can also be loss of optical properties when these clumps are incorporated into powder coatings and plastics applications.
Overcoming the disadvantages present in the prior art, embodiments of the invention disclosed herein utilize electrostatics to induce an attractive bonding force between the pigment particles. Embodiments of the disclosed invention possess the desired pigmenting characteristics without the inclusion of additives and without dry spraying being required.